Pharmacology of conjugated equine estrogens: efficacy, safety and mechanism of action

Oral conjugated equine estrogens (CEE) are the most used estrogen formulation for postmenopausal hormone therapy either alone or in combination with a progestin. CEE is most commonly used for the management of early menopausal symptoms such as hot flashes, vaginitis, insomnia, and mood disturbances. Additionally, if used at the start of the menopausal phase (age 50-59 years), CEE prevents osteoporosis and may in some women reduce the risk of cardiovascular disease (CVD) and Alzheimer's disease (AD). There appears to be a common mechanism through which estrogens can protect against CVD and AD. CEE is a natural formulation of an extract prepared from pregnant mares' urine. The product monogram lists the presence of only 10 estrogens consisting of the classical estrogens, estrone and 17β-estradiol, and a group of unique ring B unsaturated estrogens such as equilin and equilenin. The ring B unsaturated estrogens are formed by an alternate steroidogenic pathway in which cholesterol is not an obligatory intermediate. Both the route of administration and structure of these estrogens play a role in the overall pharmacology of CEE. In contrast to 17β-estradiol, ring B unsaturated estrogens express their biological effects mainly mediated by the estrogen receptor β and not the estrogen receptor α. All estrogen components of CEE are antioxidants, and some ring B unsaturated estrogens have several fold greater antioxidant activity than estrone and 17β-estradiol. The cardioprotective and neuroprotective effects of CEE appear to be, to some extent, due to its ability to prevent the formation of oxidized LDL and HDL, and by inhibiting or modulating some of the key proteases involved in programmed cell death (apoptosis) induced by the excess neurotransmitter glutamate and other neurotoxins. Selective combinations of ring B unsaturated estrogens have the potential of being developed as novel therapeutic agents for the prevention of cardiovascular disease and Alzheimer's disease in both aging women and men. This article is part of a Special Issue entitled 'Menopause'.

Structure activity relationships and differential interactions and functional activity of various equine estrogens mediated via estrogen receptors (ERs) ERalpha and ERbeta

The human estrogen receptors (ERs) alpha and beta interact with 17beta-estradiol (17beta-E2), estrone, 17alpha-estradiol, and the ring B unsaturated estrogens, equilin, 17beta-dihydroequilin, 17alpha-dihydroequilin, equilenin, 17beta-dihydroequilenin, 17alpha-dihydroequilenin, Delta8-estrone, and Delta8, 17beta-E2 with varying affinities. In comparison to 17beta-E2, the relative binding affinities of most ring B unsaturated estrogens were 2- to 8-fold lower for ERalpha and ERbeta, however, some of these unique estrogens had two to four times greater affinity for ERbeta than ERalpha. The transcriptional activity of these estrogens in HepG2 cells transfected with ERalpha or ERbeta, or both, and the secreted-alkaline phosphatase gene showed that all estrogens were functionally active. 17beta-E2 induced the activity of secreted-alkaline phosphatase by ERalpha to a level higher than any other estrogen. Activity of other estrogens was 12-17% that of 17beta-E2. In contrast, 17beta-E2 stimulated the activity of ERbeta to a 5-fold lower level than that with ERalpha, whereas the activity of other estrogens was 66-290% that of 17beta-E2, with equilenin being the most active. The presence of both ER subtypes did not alter the functional activity of 17beta-E2, although it further enhanced the activity of 17beta-dihydroequilin (200%), 17beta-dihydroequilenin (160%), and Delta8, 17beta-E2 (130%). Except for 17beta-E2, no correlation was observed between the functional activities and their binding affinities for ER. In conclusion, our results show that the effects of ring B unsaturated estrogens are mainly mediated via ERbeta and that the presence of both ER subtypes further enhances their activity. It is now possible to develop hormone replacement therapy using selective ring B unsaturated estrogens for target tissues where ERbeta is the predominant ER.

Steady-state pharmacokinetics of conjugated equine estrogens in healthy, postmenopausal women

OBJECTIVE

To determine the steady-state exposure of conjugated and unconjugated estrogen components following oral administration of conjugated equine estrogens (2 0.625-mg tablets).

STUDY DESIGN

A prospective, open-label, single-treatment study conducted at 1 clinical site with 12 healthy, postmenopausal women. Each subject received 7 daily doses of 2 conjugated equine estrogen (0.625-mg) tablets, and blood samples were taken on the last day of dosing for pharmacokinetic analysis of estrogen components.

RESULTS

The major estrogen components after estrogen dosing (as determined by steady-state plasma concentration-time curves) were estrone (100 ng x h/mL), equilin (43.1 ng x h/mL) and delta8,9-dehydroestrone (13.6 ng x h/mL). Several 17beta-reduced forms of estrogen also had consistent plasma concentrations during a steady-state dosing interval. Mean t(max) values ranged from 6.2 to 9.0 hours after dosing, and the 24-hour profiles of the various plasma estrogen concentrations at steady state showed limited fluctuations.

CONCLUSION

Oral dosing of conjugated equine estrogen at steady state resulted in consistent concentrations of estrogen components during a dosing interval.

Estrogens and menopause: pharmacology of conjugated equine estrogens and their potential role in the prevention of neurodegenerative diseases such as Alzheimer's

Menopause marks the start of a new phase in a woman's life that is associated with a decrease in circulating estrogen levels. Although the average age of women has increased from 50 to nearly 85 years, the average age at menopause has remained essentially constant at 50 years. Thus, women now spend nearly a third of their lives in an estrogen deficient state. This normal aging process in women is associated with increasing health problems such as osteoporosis, cardiovascular disease, neurodegenerative diseases, and cancer. Estrogen replacement therapy (ERT) has been shown to play an important beneficial role in the health and well being of postmenopausal women. Several estrogen preparations are available and among these conjugated equine estrogens (CEE) are most frequently used. The drug CEE, is a complex natural urinary extract of pregnant mare's urine and contains at least 10 estrogens in their sulfate ester form and these are the ring B saturated estrogens: estrone (E(1)), 17beta-estradiol (17beta-E(2)), 17alpha-estradiol (17alpha-E(2)), and the ring B unsaturated estrogens equilin (Eq), 17beta-dihydroequilin (17beta-Eq), 17alpha-dihydroequilin (17alpha-Eq), equilenin (Eqn), 17beta-dihydroequilenin (17beta-Eqn), 17alpha-dihydroequilenin (17alpha-Eqn), and Delta(8)-estrone (Delta(8)-E(1)). All of these estrogens in their unconjugated form are biologically active and can interact with recombinant human estrogen receptor alpha (ERalpha) and beta (ERbeta) with 17beta-estradiol and 17beta-dihydroequilin having the highest affinity for both receptors. A number of the ring B unsaturated estrogens had nearly twofold higher affinity for the ERbeta. The pharmacokinetics of these estrogens in postmenopausal women indicate that the unconjugated estrogens compared to their sulfated forms are cleared more rapidly. The 17-keto estrogens are metabolized to the more potent 17beta-reduced products which are cleared at a slower rate. In postmenopausal women, the extent of 17beta-activation is much higher with the ring B unsaturated estrogens than with ring B saturated estrogens. Oxidized LDL and oxidative stress are thought to contribute to both atherosclerosis and neurodegenerative disorders. Neurons in particular are at a high risk from damage resulting from oxidative stress. In vivo and in vitro studies indicate that the oxidation of LDL isolated from postmenopausal women was inhibited differently by various estrogens and other antioxidants. The unique ring B unsaturated estrogens were the most potent while the red wine component t-resveratrol was the least potent. Studies were designed to explore the cellular and molecular mechanisms that may be involved in the neuroprotective effects of CEE components. The data indicate that the neurotoxic effects of oxidized LDL and glutamate can be inhibited by various estrogens, with the ring B unsaturated estrogens being the most active. These effects are involved in the inhibition of DNA fragmentation and up-regulation of anti-apoptotic protein Bcl-2 and down-regulation of pro-apoptotic protein Bax. These combined data suggest that some of the neuroprotective benefits associated with long-term estrogen therapy may occur by the above mechanism(s). Because estrogens such as the Delta(8)-estrogens are relatively less feminizing than the classical estrogen 17beta-estradiol, they may be important in the development of more neuro-specific estrogens that will be useful in the prevention of neurodegenerative diseases, such as Alzheimer's and Parkinson disease, in both men and women.

[Does grapefruit juice increase the bioavailability of orally administered sex steroids?]

OBJECTIVE

To verify if and to which extent the interaction with grapefruit juice can increase bioavailability of orally administered sexual steroids.

DESIGN

Pilot pharmacokinetics study.

SETTING

Department of Obstetrics and Gynecology and Institute of Pharmacology, Medical Faculty, Palacký University, Olomouc; Department of Nuclear Medicine, University Hospital, Olomouc.

METHODS

2 mg of estradiol valerate and 100 mg of micronized progesterone were given to eight healthy postmenopausal volunteers. Blood samples were collected at time 0, 2, 3, 5 and 24 hours after tablets application. The same trial was repeated a week later but tablets were swallowed with 200 ml of grapefruit juice. Serum levels of estradiol and progesterone were measured by RIA. Results were statistically evaluated using the Wilcoxon's nonparametric paired test.

RESULTS

Though grapefruit juice on average slightly increased serum levels of estradiol (E2) and progesterone, this increase reached statistical significance only for the E2 level 24 hours after application of tablets. The mean area under curve (AUC) of estradiol rose significantly to 117%. The even greater increase in the mean AUC of progesterone (to 125%) was not statistically significant because of marked individual variability of response.

CONCLUSIONS

Our results suggest that grapefruit juice may increase bioavailability of orally administered estradiol and progesterone. The response varies markedly between individuals. This observation may be of some importance also for users of OC and HRT.

Evaluation of single- and multiple-dose pharmacokinetics of synthetic conjugated estrogens, A (Cenestin) tablets: a slow-release estrogen replacement product

A multiple-dose, placebo-controlled, randomized pharmacokinetic study was performed in 15 early (i.e., 1-3 years) postmenopausal women to evaluate the single and steady-state pharmacokinetics of 0.625 mg Cenestin (Synthetic Conjugated Estrogens, A) tablets, administered once daily for 90 days. Plasma concentration-time profiles for both total (conjugated and unconjugated) estrone and equilin, two major estrogens in Cenestin, were nearly superimposable between Day 1 (single dose) and Day 90 (multiple dose), indicating equivalent drug exposure from one dose to the next. For total estrone, the mean estimates of Cmax and AUC0-24 were 2.5 ng/ml and 35.0 ng x h/ml for Day 1 and 3.0 ng/ml and 39.8 ng x h/ml for Day 90, respectively. Similarly, Cmax and AUC0-24 mean values for total equilin were 1.4 ng/ml and 17.4 ng x h/ml after Day 1 and 1.5 ng/ml and 17.3 ng x h/ml after Day 90, respectively. The mean tmax value for total estrone was 8.3 hours on Day 1 and 8.6 hours on Day 90, indicating a slower rate of absorption. The average estimate for observed drug accumulation index for the 24-hour dosing interval was calculated to be 1.1 for total estrone and 1.0 for total equilin. These data, taken together, indicate a slow and steady rate of absorption, minimal drug accumulation at steady state, and consistent drug exposure between Cenestin doses.

Selective delivery of estradiol to bone by aspartic acid oligopeptide and its effects on ovariectomized mice

We have developed a novel osteotropic prodrug of estradiol (E(2)) conjugated with L-Asp-hexapeptide (E(2).3D(6)), which has very low affinity for estrogen receptors, and in this study, we examined its pharmacokinetic behavior and pharmacological potential. After a single iv injection of E(2) x 3D(6) to mice, the half-time for elimination from plasma was about 100 min; however, E(2) was selectively delivered to the bone and eliminated very slowly, declining to the endogenous level at about 7 days. After a single iv injection of E(2), the half-time in plasma was about 70 min, whereas E(2) was highly distributed to the uterus, and the bone concentration of E(2) was only slightly increased at 6 h. When E(2) (0.37 micromol/kg, sc, every third day) or E(2) x 3D(6) (0.11 to 1.1 micromol/kg, sc, every seventh day) was administered to OVX mice for 4 weeks, E(2) increased the bone mineral density (BMD) together with weights of liver and uterus, whereas E(2) x 3D(6) increased only the BMD, in a dose-dependent manner. E(2) x 3D(6) enhanced the expression of messenger RNAs of bone matrix proteins (osteopontin, bone sialoprotein, type I collagen alpha) of OVX mice at 4 h after administration, but E(2) did very slightly. These results indicate that the E(2) prodrug was delivered to the bone, where it gradually released E(2), thereby ameliorating bone loss. This acidic oligopeptide appears to be a good candidate for selective drug delivery to bone.

The pharmacokinetics and efficacy of different estrogens are not equivalent

In the next decade many women will turn to the medical community for advice on maintaining or improving health after menopause. Estrogen replacement therapy, with or without progestins, alleviates menopausal symptoms, prevents or manages osteoporosis, and reduces the increased cardiovascular disease risk that results from estrogen deficiency caused by ovarian decline. Although several estrogen replacement products are available, the pharmacokinetics and efficacy of these products may vary depending on either the estrogen formulation or the route of administration, or both. For example, oral estrogens, which elicit a marked hepatic response, induce greater beneficial effects on serum lipoproteins than transdermal estrogens, which circumvent first-pass liver metabolism. Oral conjugated estrogens and transdermal estradiol increase bone density and prevent bone loss. This article summarizes the studies comparing estrogen formulations and discusses the differential effects of various estrogen products that promote postmenopausal health.

[Influence of estrogen replacement therapies such as premarin for the measurement of estradiol]

To investigate problems associated with the measurement of estradiol 17 beta(E2) in hormone replacement therapy(HRT), five commercial immunoassay methods(Coat-A-Count E2 as the conventional method; Immulyze E2, Immuno 1 E2, Vitros E2, and HRT-E2 as the comparative methods) were used to assay E2 concentrations. Samples were obtained from 21 women who had been receiving HRT, 99 nonmedicated women, and 10 healthy men volunteers. No significant difference between the Coat-A-Count E2 and the comparative method was observed in the nonmedicated women. However, we found that the serum E2 concentration from patients taking Premarin showed a large discrepancy between the Coat-A-Count E2 method, which showed considerably higher values, and the other four methods. The reason for our conflicting results from patients with HRT was probably because the Coat-A-Count E2 detected circulating estrogen conjugates. The experimental addition of Premarin for the in vitro cross-reactivity was done. The cross-reactivity was low because a similar E2 steroid exists independently. However, the E2 serum value of the ten male volunteers after taking Premarin was elevated. The reason for this result was due to the high cross-reactivity between anti E2 polyclonal antibody and the various metabolic products of Premarin. In conclusion, the influence of Premarin should be taken into consideration when measuring estradiol concentration to monitor HRT.

Half-life of estradiol in postmenopausal women

Estrogen replacement is often advised for postmenopausal women to prevent menopausal symptoms, osteoporosis and heart disease. However, little information is available concerning the half-life of estradiol (E2) in postmenopausal women. This study was designed to determine the half-life and metabolism of transdermal E2. A prospective clinical study of 8 healthy postmenopausal women was performed in the Clinical Research Center of the Brigham and Women's Hospital. A transdermal E2 patch 0.10 mg was placed on the abdominal wall. Thirteen hours later, after an overnight fast, the E2 patch was removed and frequent blood sampling was performed over 6 h. Serum samples were assayed for E2, estrone (E1) and estrone sulfate (E1S). Serum samples were taken before E2 patch placement, for 30 min before patch removal, and for 6 h after patch removal. The basal E2 level of women prior to use of transdermal E2 was 19 +/- 2 pg/ml (mean +/- SE). Thirteen hours after transdermal E2 placement, steady state levels had been reached, with a mean E2 of 112 +/- 6 pg/ml. The mean half-life of E2 after removal of transdermal E2 was 161 min (range 107-221 min). There was a direct relationship between the subjects' weight and the half-life of E2 (r = 0.79, p = 0.02). Mean basal E1 levels were 23 +/- 5 pg/ml and mean E1 steady-state levels after E2 patch placement were 39 +/- 0.6 pg/ml. E1S levels rose from mean basal levels of 1.5 +/- 0.3 ng/ml to mean steady-state levels of 3.1 +/- 0.1 ng/ml after placement of the E2 patch. The apparent half-life of E2 after discontinuing a transdermal E2 patch is 2.7 h or 161 min.

Comparison of pharmacokinetics of a conjugated equine estrogen preparation (premarin) and a synthetic mixture of estrogens (C.E.S.) in postmenopausal women

OBJECTIVE

To compare the pharmacokinetics and relative bioavailabilities of key estrogen components of Premarin (Wyeth-Ayerst, Canada) with those of a generic conjugated estrogen preparation, C.E.S. (synthetic mixture of estrogens; ICN, Montreal, Canada) in healthy postmenopausal women.

METHODS

We conducted a randomized, single-dose, two-treatment, three-period crossover study in 41 postmenopausal women. After an oral dose (2 x 0.625 mg) of Premarin or C.E.S., plasma concentrations of unconjugated and total estrone (E(1)), equilin (Eq), 17beta-estradiol (17beta-E(2)), 17beta-dihydroequilin (17beta-Eq), Delta(8)-esterone (Delta(8)-E(1)) and Delta(8),17beta-estradiol (Delta(8),17beta-E(2)) were measured over 72 hours using gas chromatography and mass spectroscopy.

RESULTS

After administration of C.E.S., E(1), Eq, and 17beta-Eq appeared in blood at a significantly faster rate (lower t(max)) than after Premarin. The rapid appearance of estrogens after C.E.S. was associated with significantly higher (14-61%) C(max) values. In contrast to the high C(max) values, the area under the curve (AUC)(infinity) of unconjugated and total Eq, and 17beta-Eq were significantly lower after C.E.S., whereas those of E(1) were significantly higher. Although, the t(max) values for 17beta-E(2) were lower and the C(max) values higher after C.E.S., only the C(max) of unconjugated 17beta-E(2) was significantly different after Premarin. Unconjugated and total Delta(8)-E(1) and its main metabolite, Delta(8),17beta-E(2), were detectable in plasma only after administration of Premarin. The geometric mean ratio (GMR) (C. E.S./Premarin) of bioavailability parameters indicated that all C(max) and t(max) values for the unconjugated and total E(1), Eq, 17beta-E(2), and 17beta-Eq fell outside the regulatory requirement that the 90% confidence intervals of GMRs of two products be within 80% and 125%. Similarly, with the exception of total E(1) and total Eq, none of the AUC(t) or AUC(alpha) of the remaining estrogens meets the required regulatory standards of bioequivalence.

CONCLUSIONS

C.E.S. is not bioequivalent to Premarin. Because C.E.S. also is not pharmaceutically equivalent to Premarin, it cannot be assumed to be therapeutically equivalent. Until long-term clinical trials with C.E.S. demonstrate its efficacy, extrapolation of the long-term benefits described for Premarin to C.E.S. would be risky and questionable.

Pharmacokinetic comparison between Conpremin (Premarin) and a generic preparation of conjugated estrogens

OBJECTIVES

To determine the relative bioavailability of the estrogenic components of a generic brand of conjugated estrogens marketed in Chile in comparison to that of Conpremin (Premarin in the United States).

METHODS

A randomized cross-over study was conducted on 16 healthy postmenopausal women receiving single oral doses of either two Conpremin 0.625-mg tablets or two 0.625-mg tablets of the generic brand, with a 14-day wash-out interval between doses. A gas chromatography tandem mass spectrometry assay was used to determine estrogen components.

RESULTS

The peak plasma concentrations of unconjugated and total estrone and equilin, unconjugated 17 beta-dihydroequilin and 17 beta-estradiol were higher and occurred earlier with the generic conjugated estrogens than with Conpremin. The 90% confidence limits for both variables lay outside the accepted bioequivalence limits of 80-125%. Additionally, no measurable plasma concentration of unconjugated delta 8,9-dehydroestrone or 17 beta-delta 8,9-dehydroestradiol was seen after administration of the generic conjugated estrogens.

CONCLUSIONS

These pharmacokinetic results indicate that the generic tablets do not have the modified-release characteristics of Conpremin tablets. In addition, the absence of delta 8,9-dehydroestrone and 17 beta-delta 8,9-dehydroestradiol in the plasma indicates that the generic form is not compositionally equivalent to Conpremin.

Pharmacokinetics and pharmacodynamics of a novel estrogen delta8-estrone in postmenopausal women and men

Recently a tenth equine estrogen, identified as the sulfate ester of delta8-estrone has been reported to be present in Premarin (a conjugated equine estrogen preparation), and because of its unique ring B unsaturated structure (conjugated double bond in the B ring), we have, in the present study, determined its pharmacokinetics in postmenopausal women and men, its interaction with uterine estrogen receptors and its uterotropic activity. After the administration of [14C]delta8-estrone, blood was drawn at various time intervals, and the plasma fractionated into the unconjugated sulfate and glucuronide fractions. The disappearance of radioactivity as delta8-estrone from plasma can be described as a function of two exponentials. The half-lives of the first and second components were 5+/-0.2 and 40.4 min, respectively. The mean metabolic clearance rate calculated (MCR), was 1711+/-252 l/d m2. From the unconjugated fraction, delta8-17beta-estradiol was also isolated and identified. From the sulfate conjugated fraction, delta8-estrone sulfate and delta8-17beta-estradiol sulfate were isolated in almost equal amounts. No other metabolites of delta8-estrone was detectable in the plasma. Both delta8-estrone and delta8-17beta-estradiol bind with human endometrial and rat uterine estrogen receptors with high affinity. The binding affinities of delta8-17beta-estradiol for human endometrial and rat uterine cytoplasmic receptors were 4 and 25 times higher than those of the parent estrogen delta8-estrone, respectively. Administration of delta8-estrone and delta8-17beta-estradiol (2 microg/100 g body weight) to immature rats significantly (P< 0.05) increased the uterine weight compared to the controls. These data demonstrate that delta8-estrone has estrogenic activity, and that it is further metabolized in man to a single more potent estrogen, delta8-17beta-estradiol. The extent of this activation by 17beta-reduction appears to be greater than that observed with other estrogens. Both estrogens circulate as sulfate conjugates and are very slowly eliminated from the circulation. These data further suggest that delta8-estrone and its major metabolite delta8-17beta-estradiol can contribute to the overall in vivo biological effects of Premarin.

Transfer of [3H]estrone-[35S]sulfate across guinea pig fetal membranes

The possible role of fetal membrane deconjugating activity in the movement of a charged steroid conjugate between fetal and maternal compartments was investigated. The ability of amnion and chorion laeve to transfer [3H]estrone-[35S]sulfate was assessed in both orientations of guinea pig tissue at 45 days and near parturition. While early amnion was impermeable, late tissue transferred approximately 50% (w/w) of the substrate in a bidirectional process that was non-saturable and independent of either deconjugation or ATP. Transfer across early chorion was similar to late amnion. Saturation curves from each tissue were superimposable, as were those of the time course. Transfer across both early and late chorion proceeded in the absence of deconjugation, with no effect of tissue orientation or ATP depletion. However, late chorion exhibited a decrease in estrone-sulfate transfer, as verified by concentration dependency and time course analyses, though transport across the tissue remained non-saturable. The results in amnion were congruous with the presence and absence of tight junctions in the epithelium of early and late tissue, respectively. However, sulfoconjugate transfer across early chorion proceeded in the presence of a paracellular barrier, suggesting specialized regulation of the transport process which extended late into gestation.

Pharmacokinetics of orally administered estradiol valerate. Results of a single-dose cross-over bioequivalence study in postmenopausal women

A randomized, single-dose cross-over study in 32 postmenopausal women was performed to demonstrate bioequivalence of two estradiol valerate containing formulations (first sequence of Klimonorm as test preparation). The serum levels of estradiol, free and conjugated estrone were measured until 48 h after an oral dosage of 4 mg estradiol valerate (CAS 979-32-8). The mean AUC(0-48) of estradiol was calculated as 1006.6 +/- 479.4 h x pg x ml-1 (Test) and 1015.2 +/- 555.2 h x pg x ml-1 (Reference). The corresponding (AUC(0-48) of the active metabolite, free estrone, exceeded that of estradiol at 3578.3 h x pg x ml-1 (Test) and 3485.1 h x pg x ml-1 (Reference). Much higher was the AUC(0-48) for conjugated estrone at 132.4 h x ng x ml-1 (Test) and 133.6 h x ng x ml-1 (Reference). Mean estradiol Cmax values of 39.8 +/- 17.7 pg/ml (Test) and 42.9 +/- 21.0 pg/ml (Reference) were attained 8.2 +/- 4.5 h (Test) and 10.0 +/- 5.9 h (Reference) after the administration of 4 mg estradiol valerate. Maximal free estrone concentrations of 163 pg/ml (Test) and 174.3 pg/ml (Reference) were reached after 7.2 h (Test) and 7.5 h (Reference). Maximal conjugated estrone concentrations of 15.5 ng/ml (Test) and 16.2 ng/ml (Reference) were reached after 2.4 h (Test) and 2.0 h (Reference). The terminal elimination half-life of estradiol was calculated at 16.9 +/- 6.0 h (Test) and 15.0 +/- 4.8 h (Reference), that of free estrone at 16.3 h (Test) and 13.5 h (Reference), that of conjugated estrone at 11.8 h (Test) and 10.6 h (Reference). After logarithmic transformation, the 90% confidence intervals of the AUC(0-48) and Cmax ratios for estradiol and also for the metabolites (free and conjugated estrone) were within the acceptance ranges for bioequivalence. Therefore the test preparation and the reference preparation are bioequivalent.

Enterohepatic cycling and pharmacokinetics of oestradiol in postmenopausal women

The pharmacokinetics and enterohepatic cycling of oestradiol have been studied after three oral, single-dose administrations of equimolar doses of oestradiol alone, oestradiol plus desogestrel and oestradiol valerate, in a 3-way cross-over mode in 18 healthy postmenopausal women. Oestradiol was readily absorbed and metabolized to oestrone, which reached much higher serum concentrations (140pgmL(-1)) than its parent compound (35pgmL(-1)). All three formulations had the same kinetic profile and were bioequivalent on testing. Noticeable first and second absorption phases were apparent from the oestradiol and oestrone serum concentration-time curves for all oestradiol formulations. The mean serum concentration-time curves of the metabolite oestrone (corrected for endogenous oestrone) showed a second maximum at approximately 25h. By means of line feathering, serum concentration-time curves were constructed which belonged to the first, second and third phases of absorption. The maximum serum concentration, Cmax, of the second absorption or recirculation of oestrone was 20% that of the first, and the Cmax of the third circulation was 50% that of the second. The areas under the serum-concentration-time curves (AUC) for the second and third recirculations were similar-each comprised 12-13% of the total AUC. The oral clearance values of the recirculations were constant (590Lh(-1)). Enterohepatic recirculation of endogenous compounds is aimed at maintaining a steady-state serum concentration for immediate use and hydrolysis in the target organs. It is concluded that exogenously added oestradiol and its metabolites follow the recirculation pathways of the endogenous oestrogen pool.

Pharmacokinetics and pharmacodynamics of conjugated equine estrogens: chemistry and metabolism

Conjugated equine estrogens (Premarin), are used extensively for estrogen replacement therapy and prevention of osteoporosis and cardiovascular disease in postmenopausal women. Premarin contains at least 10 estrogens that are the sulfate esters of the ring B saturated estrogens: estrone, 17beta-estradiol, 17alpha-estradiol, and the ring B unsaturated estrogens: equilin, 17beta-dihydroequilin, 17alpha-dihydroequilin, equilenin, 17beta-dihydroequilenin, 17alpha-dihydroequilenin, and delta-8-estrone. Bioassays and estrogen receptor binding studies indicate that all 10 estrogens are biologically active. Moreover, individual components, such as equilin sulfate, delta-8-estrone sulfate, 17beta-dihydroequilin sulfate and estrone sulfate, have potent estrogenic effects. Estrogen sulfates can be absorbed directly from the gastrointestinal tract; however, hydrolysis of the sulfates also occurs in the gastrointestinal tract, and the unconjugated estrogens formed are readily absorbed. After absorption, these estrogens are sulfated rapidly and circulate in this form. The pharmacokinetics of these estrogens indicate that the unconjugated estrogens are cleared from the circulation at a faster rate than their sulfate ester forms. In postmenopausal women, the 17-keto derivatives of these estrogens are metabolized to the more potent 17beta-reduced products. The extent of this activation is nearly 10 times higher with some ring B unsaturated estrogens. The 17beta-reduced metabolites are cleared from the blood at a slower rate than their corresponding 17-keto derivatives. In the human endometrium, equilin is metabolized to 2-hydroxy and 4-hydroxy equilin, with 2-hydroxylation being predominant. In contrast, 2-hydroxy and 4-hydroxy estradiol are formed in equal amounts. Similarly, 16alpha-hydroxylation occurs with both types of estrogens; however, with the ring B saturated estrogens, the 17-keto steroid 16alpha-hydroxy estrone was the major urinary metabolite, whereas with the ring B unsaturated estrogens, the 17beta-reduced steroids, such as 16alpha-hydroxy-17beta-dihydroequilin and 16alpha-hydroxy-17beta-dihydroequilenin, were the major metabolites. This difference in metabolism may be important as it has been suggested that 16alpha-hydroxy estrone (alpha-ketol structure) can form covalent adducts with macromolecules and that it may be oncogenic. These types of interactions will not occur with the 16alpha-hydroxylated-17beta-reduced metabolites of ring B unsaturated estrogens. Since all of the estrogens present in Premarin have estrogenic activity, the pharmacological effects of Premarin are a result of the sum of these individual activities. Therefore, preparations lacking some of these important components may not offer the same degree of beneficial effects as Premarin.

Single-dose pharmacokinetics of sublingual versus oral administration of micronized 17 beta-estradiol

OBJECTIVE

To investigate the pharmacokinetic profiles of different doses of micronized 17 beta-estradiol administered by oral or sublingual routes.

METHODS

Single doses of micronized 17 beta-estradiol were administered orally (1 mg, 0.5 mg) or sublingually (1 mg, 0.5 mg, 0.25 mg) to six postmenopausal women in a randomized clinical trial. We calculated pharmacokinetic parameters for estradiol (E2) and estrone (E1) of maximum serum concentration, time to maximum serum concentration, terminal half-life, area under the concentration curve, and oral clearance. Serum levels of E1 sulfate also were compared at 4, 12, and 24 hours after dosing.

RESULTS

Sublingual administration resulted in rapid absorption with significantly higher E2 levels than did comparable oral dosing. Estrone levels did not vary with route of administration but correlated with the dosage administered. Estrone sulfate levels correlated with the dosage administered and also tended to be higher with sublingual administration. Sublingual administration resulted in a significantly lower E1 to E2 ratio during the 24 hours than did oral administration.

CONCLUSION

Sublingual administration of micronized 17 beta-estradiol results in a rapid, burst-like absorption into the systemic circulation, yielding high E2 levels that fall rapidly over the first 6 hours.

Uptake of sulfate conjugates by isolated rat hepatocytes

The uptake of estrone sulfate (E1S; 1 to 400 microM), harmol sulfate (HS; 5 to 900 microM), and 4-methylumbelliferyl sulfate (4MUS; 5 to 1000 microM) was investigated in isolated rat hepatocytes in the presence or absence of inhibitors. Uptake of all of the sulfate conjugates was rapid and exhibited saturation kinetics, best characterized by saturable and nonsaturable (linear transmembrane clearance) transport systems. The KM's were: 16 +/- 6, 123 +/- 28, and 64 +/- 6 microM for E1S, HS, and 4MUS, respectively, with corresponding Vmax's of 0.85 +/- 0.56, 0.48 +/- 14, and 0.42 +/- 0.07 nmol/min/10(6) cells. The nonsaturable uptake clearances, which displayed concentration-independent uptake, were 3 +/- 2, 1 +/- 0.1, 0.5 +/- 0.1 microliter/min/10(6) cells, respectively. Uptake of E1S was inhibited by ouabain (1 mM) and replacement of sodium by choline, whereas HS was insensitive to the addition or substitution. Uptake of both E1S and HS was significantly reduced by metabolic inhibitors (antimycin A, 2.7 microM, rotenone, 30 microM, and KCN, 2 mM) and temperature reduction (from 37 to 27 degrees C). 4,4'-Diisothiocyanostilbene-2-2-'disulfonic acid (2 mM), an inhibitor of anion transport, reduced E1S and HS uptake; E1S uptake was also reduced by HS. HS uptake by both saturable and nonsaturable transport components was depressed by 4MUS (300 microM); the apparent KM was increased by 83% while the Vmax remained unaltered, and the nonsaturable component was decreased by 48%. The data strongly suggest that multiple pathways exist for the uptake of E1S, HS, and 4MUS. E1S uptake is sodium-dependent, requires energy, and is inhibited by anions such as 4,4'diisothiocyanostilbene-2-2'-disulfonic acid and other sulfate conjugates. HS uptake, while being energy dependent, is not sodium dependent, and is inhibited by 4MUS in a competitive fashion. At least one of these pathways is shared.

Metabolism of equilin sulfate in the dog

The metabolism of equilin sulfate was determined in female dogs receiving 2.5 mg/kg of [3H]equilin sulfate alone or in a preparation that contained all the components that are present in the conjugated equine estrogen product Premarin. The pharmacokinetic parameters of total radioactivity indicated that the drug is rapidly absorbed and it has a moderate half-life in plasma. The total radioactivity in plasma following administration of [3H]equilin sulfate as part of a mixture of conjugated equine estrogens had significantly lower peak concentration (Cmax), a lower area under the curve (AUC), a longer terminal half-life (t1/2) and a longer mean residence time (MRT) than when [3H]equilin sulfate was given alone, indicating that the other components in the conjugated equine estrogen preparation altered the pharmacokinetics of equilin sulfate. An average of 26.7 +/- 4.4% of the administered radioactive dose was excreted in urine of dogs receiving [3H]equilin sulfate. Again, a significantly lower percentage (21.4 +/- 6.3%, P = 0.023) was eliminated in urine of dogs receiving [3H]equilin sulfate in the conjugated equine estrogen preparation, indicating that the absorption of equilin sulfate was perhaps altered by the other components in the conjugated equine estrogen preparation. Metabolite profiles of plasma and urine were similar. Equilin, equilenin, 17 beta-dihydroequilenin, 17 beta-dihydroequilin, 17 alpha-dihydroequilenin and 17 alpha-dihydroequilin were present in both matrices. 17 beta-Dihydroequilin and equilin were the two major chromatographic peaks in plasma samples. 17 beta-Dihydroequilenin and 17 beta-dihydroequilin were the major metabolites in urine. In conclusion, following oral administration of [3H]equilin sulfate to dogs, the radioactivity is rapidly absorbed. The disposition of equilin sulfate is altered by the other components that are present in the conjugated equine estrogen preparation Premarin. The reduction of the 17-keto group and aromatization of ring-B are the major metabolic pathways of equilin in the dog.

Clinical experience with a seven-day estradiol transdermal system for estrogen replacement therapy

OBJECTIVE

To describe the efficacy, safety, and wearability of estrogen replacement therapy of a 7-day estradiol transdermal system (Climara), developed using new drug-in-adhesive technology.

STUDY DESIGN

The pharmacokinetics of the 7-day system were investigated in single- and multiple-dose studies, a relative bioavailability study of the two patch sizes, and comparative studies with the twice-weekly transdermal system (Estraderm). Safety and efficacy in the treatment of vasomotor symptoms compared with conjugated equine estrogens (Premarin) and placebo were evaluated in two 11-week, randomized, double-blind, multicenter trials in 603 women; the data are combined in this report. Irritation and adhesion were also evaluated in comparative studies with Estraderm, Micropore (an inert once-weekly tape), and placebo controls.

RESULTS

Blood levels were sustained for the full 7 days of patch wear, there was no drug accumulation, and a physiologic estrone to estradiol ratio was maintained. Pharmacokinetics studies showed dose proportionality of the 0.05 and 0.1 mg/day patches. Both patch sizes significantly decreased the frequency of hot flushes compared with placebo and were comparable with conjugated equine estrogens. There was a statistically significant difference between the two patch sizes. The mean overall decline in the hot flush rate was 74.6% for the 0.1 mg patch versus 64.5% for the 0.05 mg patch (p < or = 0.05). The combined data also showed that the onset of efficacy is within 1 to 2 weeks after the start of therapy and that efficacy is fully sustained during the 7-day patch wear period with some diminution of effect during the treatment-free week of each cycle. Treatment was well tolerated. Adverse events led to withdrawal from the studies in 8.9% of subjects. In most of these (6.8% of subjects), the cause was adverse skin reactions. Skin irritation was similar to Estraderm in comparative studies, whereas adhesion was significantly better with Climara.

CONCLUSION

The Climara patch delivers estradiol for a full 7 days. Clinical efficacy of both patch sizes is comparable with currently accepted therapy and is sustained for the entire week of patch wear. A significant difference in response between the two doses supports dose titration. The patch is well tolerated and has excellent adhesion.

Vaginal administration of low-dose conjugated estrogens: systemic absorption and effects on the endometrium

OBJECTIVE

To test the hypothesis tha a very-low-dose regimen of vaginal estrogen would provide effective relief from atrophic vaginitis without endometrial proliferation.

METHODS

Twenty postmenopausal women with symptoms, signs, and cytologic evidence of atrophic vaginitis were enrolled. Each subject was treated with 0.3 mg of conjugated estrogens, administered vaginally 3 nights per week for 6 months. We examined the following outcomes: symptoms, vaginal cellular (cytologic) maturity, endometrial histology, sonographic evaluation of endometrial thickness, Doppler measures of uterine artery blood flow, and serum levels of estrone and estradiol. Pre- and post-treatment data were compared for each subject.

RESULTS

Satisfactory relief of symptoms occurred in 19 of 20 cases. Vaginal cellular maturation improved significantly with therapy (P < .01). There were no significant changes in endometrial thickness, uterine artery blood flow, or serum estrogen levels. Endometrial proliferation was observed in one case.

CONCLUSIONS

Relief from atrophic vaginitis can be achieved with 0.3 mg of conjugated estrogens administered vaginally three times per week. Endometrial proliferation may occur at this low dose, albeit rarely.

The metabolism of estrone sulfate in the female rhesus monkey

In order to study the metabolism of estrone sulfate in the adult female rhesus monkey, we gave four monkeys a pulse injection of [3H]estrone sulfate and obtained blood samples at 15, 30, 60, 120, 300, and 1,440 minutes after the pulse. All blood samples were analyzed for [3H]estrone sulfate. The mean +/- SE for the initial volume of distribution was 4.6 +/- 0.9 L. The mean metabolic clearance rate (MCR) was 42.0 +/- 2.9 L/day. In addition, 2 monkeys were infused for 240 minutes with [3H]estrone sulfate and 5 monkeys were infused for 240 minutes with [3H]estrone sulfate/[14C]estrone. Three blood samples were obtained during the last hour of the infusions and analyzed for radioactivity as estrone sulfate, estrone, and estradiol, and MCRs, conversion ratios, and [rho]BB values were calculated. The mean +/- SE for the MCR was 67.5 +/- 8.3 L/day, and for the conversion ratio, estradiol to estrone sulfate was 0.054 +/- 0.016. The mean [rho]BB value for estrone sulfate conversion to estrone was 43.6 +/- 3.4% and for estrone conversion to estrone sulfate was 33.5 +/- 6.6%. Thus estrone sulfate is cleared slowly and is converted to both estrone and estradiol. The hydrolysis of estrone sulfate to estrone is not significantly different than the conversion of estrone to estrone sulfate.

Pharmacokinetics of 17 beta-dihydroequilin sulfate and 17 beta-dihydroequilin in normal postmenopausal women

The MCRs of 17 beta-dihydroequilin sulfate and 17 beta-dihydroequilin were determined in normal postmenopausal women by single iv injection of either 17 beta-[3H]dihydroequilin sulfate ([3H]17 beta-EqS) or 17 beta-[3H]dihydroequilin ([3H]17 beta-Eq). After the administration of [3H]17 beta-EqS, blood was drawn at various time intervals, and the plasma obtained was fractionated into the unconjugated, sulfate, and glucuronide fractions. The bulk of radioactivity was present in the sulfate fraction, and from this [3H]17 beta-EqS, [3H]equilin sulfate, [3H]equilenin sulfate, and 17 beta-[3H]dihydroequilenin sulfate were isolated and purified, and their concentrations were measured. The disappearance of [3H]17 beta-EqS from plasma can be described as a function of two exponentials. The half-life of the initial fast component was 5 +/- 0.2 min; this component represents the distribution and transfer from a space, with a mean volume (V1) of 6 +/- 0.5 L. The value for the rate constant (k) of total removal from this space was 300 +/- 20 U/day, of which 35 +/- 2% was irreversible. The mean half-life of the slower component of 17 beta-EqS was 147 +/- 15 min, and the mean MCR was 376 +/- 93 L/day.m2. Similarly, after the administration of [3H]17 beta-Eq, the disappearance of radioactivity as 17 beta-Eq from plasma also had two components. The half-lives of the fast and slow component were 5.5 +/- 0.8 and 45 +/- 2.0 min, respectively. The MCR of 17 beta-Eq was 1252 +/- 103 L/day.m2. From both series of experiments, unconjugated and sulfate-conjugated equilin, equilenin, and 17 beta-dihydroequilenin were isolated and purified, and their concentrations were measured. No 17 alpha-reduced metabolites were detected. These results indicate that 17 beta-EqS is cleared twice as fast as equilin sulfate (MCR, 176 L/day.m2), whereas the more potent estrogen 17 beta-Eq is cleared 2 times slower than equilin. The slower elimination and greater estrogenic activity of 17 beta-Eq support the hypothesis that the major in vivo activity of equilin sulfate present in conjugated equine estrogen preparations is expressed via its metabolites 17 beta-EqS and 17 beta-Eq.

Pharmacokinetics of oestrogens and progestogens

There are large inter- and intra-individual variations in the serum concentrations of natural and synthetic sex steroids irrespective of the route of administration. Oral ingestion of steroids has a stronger effect on hepatic metabolism than parenteral administration, as the local concentration in liver sinusoids are 4-5 times higher during the first liver passage. Oestradiol and oestrone are interconvertible, dependent on the local concentrations in liver and target organs, and oestrone sulphate serves as a large reservoir. The oestrone/oestradiol ratio has no physiological significance, as oestrone is only a weak oestrogen. Oestrone is both a precursor and a metabolite of oestradiol. Oestriol is extensively conjugated after oral administration. Therefore, the oestriol serum levels are similar after oral intake of 10 mg and after vaginal application of 0.5 mg oestriol resulting in similar systemic effectiveness. Conjugated oestrogens can easily enter the hepatocytes but are hormonally active only after hydrolyzation into the parent steroids. Ethinylestradiol which exerts strong effects on hepatic metabolism and inhibits metabolizing enzymes, should not be used for hormone replacement therapy. Among the progestogens, the progesterone derivatives have less effects on liver metabolism than the norethisterone derivatives (13-methyl-gonanes and 13-ethyl-gonanes). The highly potent 13-ethyl-gonanes are effective at very low doses, because of a slow inactivation and elimination rate due to the ethinyl group.

Dose-effect and pharmacokinetics of estrogens given to correct bleeding time in uremia

Conjugated estrogens have a significant and long-lasting effect in shortening bleeding time in patients with end-stage renal disease. The studies so far available indicate that repeated estrogen administrations are necessary to short bleeding time in uremia in a dose range of 95 to 325 mg. With the present study we wanted to establish whether single or repeated doses are required to induce a significant shortening of bleeding time in uremia, and the minimum cumulative dose of conjugated estrogens necessary to control bleeding time for a prolonged period of time, and to check whether the prolonged effect of estrogens on bleeding time in uremia is due to an accumulation of the drug or its metabolites in the blood. Fifteen uremics on chronic hemodialysis were studied. A pilot study carried out in five uremic patients indicated that single or repeated estrogen infusions of 0.3 mg/kg did not significantly influence bleeding time values. Therefore the subsequent studies have been carried out using daily infusion of 0.6 mg/kg. A single estrogen infusion of 0.6 mg/kg shortened bleeding time in all patients. The effect was transient and bleeding time returned to pre-infusion values within 72 hours. A 50% decrease of bleeding time or a shortening of bleeding time more than 30 to 15 minutes or less was obtained in all patients with four or five infusions (0.6 mg/kg) spaced 24 hours apart. The effect lasted for 14 days. At day 25 from the last infusion all the patients had bleeding time values comparable with the pre-infusion ones.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of a cecal volume-reducing intestinal microflora on the excretion and entero-hepatic circulation of steroids and bile acids

From mouse fecal material we have isolated four strictly anaerobic bacteria which, when associated with germfree mice or rats, reduced the cecal volume by 80 and 60%, respectively. This cecal volume-reducing flora did not metabolize estrone-3-sulfate, taurolithocholate-3-sulfate or taurolithocholate but gnotobiotic rats associated with this particular flora (CRF-rats) excreted these compounds faster in feces plus urine than did germfree rats. The time needed for 50% excretion (t1/2) of orally administered estrone-3-sulfate was 32 h in germfree rats versus 13 h in CRF rats; for intraperitoneally injected taurolithocholate-3-sulfate the t1/2 was 63 h in germfree versus 17 h in CRF rats and for taurolithocholate the t1/2 was 199 h in germfree and 96 h in CRF rats. Association of germfree rats with the cecal volume-reducing flora did not change the cecal absorption rate of estrone-3-sulfate, but shortened the 50% small intestinal transit time of [14C]PEG from 10 to 3 h; a value also found in conventional rats. These results stress the important influence of the intestinal microflora on the absorption and excretion of steroids via its effect on the physiology of the whole intestinal tract and point to the deficiencies inherent to the use of germfree animals in excretion studies.